Nosema Bee Disease
Nosema
is contracted by
adult bees ingesting nosema spores in contaminated
food or water or through close contact with contaminated colonies such as
exposure to infected combs. The spores germinate in the stomach and invade
cells along the mid intestine. The organism matures and produces more spores
which are released when infected cells rupture. Spores are excreted in the faeces. Dysentery symptoms are commonly accompanied by
crawling symptoms in affected bees. Adult bees die off prematurely. Infected
nurse bees do not fully develop and infected queens can die suddenly. In
extreme cases, scouring can be observed over the front of hives. Generally the
hive strength is reduced and likewise hive
productivity.
Cause
The
disease is caused by the spore forming microsporidian,
Nosema apis.
Spores of this organism can only be seen using a light microscope.
Symptoms
The
symptoms of Nosema are relatively nonspecific, which
makes it difficult to distinguish from other diseases of the honeybee. It
arises mostly in the spring after periods of bad weather, although it may also
be a winter disease that is only noticed in the spring when beekeepers first
inspect their hives. The female worker bees are most strongly afflicted, less
so the drones. The queen bee is rarely infected since afflicted bees rarely
participate in feeding the queen. The most notable symptom is [dysentery]. This
appears as yellow stripes on the outside of the hive and in severe cases,
inside the hive. Bees may be unable to fly ("crawling") due to
disjointed wings. Further symptoms include increased girth of the abdomen,
missing sting reflex, and early replacement of the queen. If the queen is
infected, her ovaries degenerate and egg production drops due to atrophy of the
oocytes, after which she is likely to be superseded.
Effect of nosema on
bees
·
hypopharyngeal (brood food) glands of infected nurse bees lose the
ability to produce royal jelly which is fed to honey bee brood
·
a
high proportion of eggs laid by the queen of a infected colony may fail to
produce mature larvae
·
young
infected nurse bees cease brood rearing and turn to guard and foraging duties
usually undertaken by older bees
·
life expectancy of infected bees is
reduced. In spring and summer, infected bees live half as long as non-infected
bees
·
infected
queens cease egg-laying and die within a few weeks
·
infected
pupae are resistant to infection
·
an increase of dysentery in adult
bees although nosema is not the prime cause of
dysentery.
Effects on the hive
Nosema spores are spread to other colony
members through fecal matter. The disease impairs the digestion of pollen,
thereby shortening the life of the bee. A greater proportion of worker bees
become infected than drones or queens, probably due to the comb-cleaning
activities of young bees in which drones and queens do not participate. Nosema-infected bees do not attend or feed the queen to the
same extent as healthy bees, which helps the queen to escape infection. When
the queen becomes infected, her ovaries degenerate and her egg-laying capacity is reduced due to atrophy of the oocytes.
Queens that become infected by the parasite during the brood-rearing season are
superseded by the bees.
The
seasonal trend of typical infections exhibits low levels during summer, a small
peak in autumn, and a slow rise of infection during winter. It is more common
during times of confinement - winter and spring. In the spring, the level of
infection increases rapidly as brood-rearing starts and while flight
possibilities are still limited. Colonies in northern climates are more
seriously affected than colonies in the south because of the increased amount
of time bees are confined in the hive. Nosema, if
left untreated, can cause queen supersedure, winter
kills, reduced honey yields, and dwindling populations.
Diagnosis
A
microscopic examination is the only reliable test for the presence of nosema disease. Thirty to fifty adult suspect bees (sick or
only recently dead) or bees collected from the top bars of the frame should
placed in a clean jar, preserved with methylated
spirits and sent to the laboratory by courier for testing. Nosema
species can be detected easily under a 400 magnification microscope. However,
differentiation of N. apis
from N. ceranae requires a PCR (polymerase chain
reaction) test. This test is more expensive and details should be discussed
with the laboratory if nosema species identification
is required.
Treatment
Treatment
with the antibiotic Fumidil B (prepared from Aspergillus fumigatus, the
causative agent of stonebrood), inhibits the spores
reproducing in the ventriculus, but does not kill the
spores. A disinfection of the honeycombs and utensils is recommended for an
extensive disease outbreak. The spores are sensitive to chemicals such as
acetic acid and formaldehyde, and physical radiation: ultrasonic and gamma
radiation. Heat treatment in 49 °C (120 °F) for 24 hours can be used to kill
the spores on contaminated equipment.
Control
Australian
beekeepers use management practices to minimize the incidence of nosema. Chemical treatments for control of nosema are not registered in Australia for use in honey
production beehives. Use of any such treatment is illegal and could result in
unacceptable residues in extracted honey.
·
maintain colonies with queens with good
egg-laying potential. Colonies prepared for winter should have a good
population of young bees
·
ensure colonies have adequate supplies
of high protein pollen in autumn. This will help to ensure good populations of
young bees
·
ensure hives prepared for winter have
good supplies of honey. Studies have shown that colonies with generally with
half, or more, of honey had lower spore counts compared to colonies wintered
with less honey.
·
place the hives in a sunny position in
the cooler months of the year. Choose apiary sites that have good air drainage
and protection from cold winds. Avoid cool shady and damp sites. Research has
shown that the level of nosema infection in a colony
can be reduced from about 85% to zero by placing the hive in a sun trap where
it obtains maximum sun and maximum shelter from cold winds
·
maintain winter colonies in a minimum of
hive space so they are compact and warm. Remove supers (boxes) of combs not
required by the bees
·
avoid
colony stress which can be caused by excessive opening of the hive,
manipulation of combs, feeding and relocating colonies
·
avoid
stagnant water sources which may become contaminated by dead bees and bee
excreta
·
minimise the number of squashed bees
during normal hive management. Any infection will be spread when their remains
are cleared away by hive cleaning bees
·
replace old, dark brood combs to lower
the number of spores in the hive, although this will never totally eliminate
the disease. Many beekeepers remove two or more old combs from the brood nest
each spring, replacing them with sheets of beeswax foundation available from
beekeeping supply shops.